coresight: Add try_get_module() in coresight_grab_device()

When coresight device is in an active session, driver module of
that device should not be removed. Use try_get_module() in
coresight_grab_device() to prevent module to be unloaded.
Use get_device()/put_device() to protect device data
in the middle of active session.

Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200928163513.70169-7-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight.c

@@ -629,13 +629,45 @@ struct coresight_device *coresight_get_sink_by_id(u32 id)
 	return dev ? to_coresight_device(dev) : NULL;
 }
 
+/**
+ * coresight_get_ref- Helper function to increase reference count to module
+ * and device.
+ * Return true in successful case and power up the device.
+ * Return false when failed to get reference of module.
+ */
+static inline bool coresight_get_ref(struct coresight_device *csdev)
+{
+	struct device *dev = csdev->dev.parent;
+
+	/* Make sure the driver can't be removed */
+	if (!try_module_get(dev->driver->owner))
+		return false;
+	/* Make sure the device can't go away */
+	get_device(dev);
+	pm_runtime_get_sync(dev);
+	return true;
+}
+
+/**
+ * coresight_put_ref- Helper function to decrease reference count to module
+ * and device. Power off the device.
+ */
+static inline void coresight_put_ref(struct coresight_device *csdev)
+{
+	struct device *dev = csdev->dev.parent;
+
+	pm_runtime_put(dev);
+	put_device(dev);
+	module_put(dev->driver->owner);
+}
+
 /*
  * coresight_grab_device - Power up this device and any of the helper
  * devices connected to it for trace operation. Since the helper devices
  * don't appear on the trace path, they should be handled along with the
  * the master device.
  */
-static void coresight_grab_device(struct coresight_device *csdev)
+static int coresight_grab_device(struct coresight_device *csdev)
 {
 	int i;
 
@@ -644,9 +676,20 @@ static void coresight_grab_device(struct coresight_device *csdev)
 
 		child  = csdev->pdata->conns[i].child_dev;
 		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
-			pm_runtime_get_sync(child->dev.parent);
+			if (!coresight_get_ref(child))
+				goto err;
 	}
-	pm_runtime_get_sync(csdev->dev.parent);
+	if (coresight_get_ref(csdev))
+		return 0;
+err:
+	for (i--; i >= 0; i--) {
+		struct coresight_device *child;
+
+		child  = csdev->pdata->conns[i].child_dev;
+		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
+			coresight_put_ref(child);
+	}
+	return -ENODEV;
 }
 
 /*
@@ -657,13 +700,13 @@ static void coresight_drop_device(struct coresight_device *csdev)
 {
 	int i;
 
-	pm_runtime_put(csdev->dev.parent);
+	coresight_put_ref(csdev);
 	for (i = 0; i < csdev->pdata->nr_outport; i++) {
 		struct coresight_device *child;
 
 		child  = csdev->pdata->conns[i].child_dev;
 		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
-			pm_runtime_put(child->dev.parent);
+			coresight_put_ref(child);
 	}
 }
 
@@ -682,7 +725,7 @@ static int _coresight_build_path(struct coresight_device *csdev,
 				 struct coresight_device *sink,
 				 struct list_head *path)
 {
-	int i;
+	int i, ret;
 	bool found = false;
 	struct coresight_node *node;
 
@@ -712,11 +755,14 @@ out:
 	 * is tell the PM runtime core we need this element and add a node
 	 * for it.
 	 */
+	ret = coresight_grab_device(csdev);
+	if (ret)
+		return ret;
+
 	node = kzalloc(sizeof(struct coresight_node), GFP_KERNEL);
 	if (!node)
 		return -ENOMEM;
 
-	coresight_grab_device(csdev);
 	node->csdev = csdev;
 	list_add(&node->link, path);